This invention relates to a method and apparatus for forming electrode components and, in particular, electrode components comprised of a fibrillated polymer binder which holds the electrode active material.
Electrodes which employ a fibrillated polymer binder for holding the electrode active material are known in the art. These electrodes are used in fuel cells and batteries and usually employ polytetrafluorethylene (PTFE) as the polymer binder. To ensure proper operation of the electrode, the weight percent of the polymer binder is normally selected to be less than the combined weight percent of the active and other materials of the electrode. Thus, for battery electrodes, the polymer binder is usually less than about 10 weight percent of the combined component materials making up the electrode and for fuel cells less than about 50 weight percent.
In the formation of electrodes of this type, the usual practice is to first mix the active material, polymer binder and any other component materials in a batch type process during which the materials are placed in a mixer and the polymer is subjected to high shear stresses. These shear stresses cause the desired fibrillation of the polymer binder and a product results which is an intimate mixture of the fibrillated polymer, active material and other components.
Following this batch processing, the mixture is shaped and formed as desired. If the material is to be formed as a sheet, this can be carried out by pressing the mixture or calendering same. Alternatively, the mixture can be extruded to any shape and then cut into sheets.
Czechoslovakian Patent No. 209,356 discloses another type of process for forming electrodes of this type in which a mixture of active material, a liquid plasticizer and a plastic bonding agent is formed and extruded through an extruder nozzle at normal temperature to form an electrode tube. In this process, the size and shape of the plastic binder particles are such that during the extruding process the particles are geometrically oriented into a fiber like shape which gives mechanical strength and optimum ion exchange properties to the electrode tube.
While these procedures of electrode formation provide the desired electrodes, efforts are still underway to develop quicker and less labor intensive procedures which result in electrodes with enhanced and more controllable fibrillation of the polymer binder.
It is, therefore, a primary object of the present invention to provide a method and apparatus for forming a cohesive fibrillated polymer electrode component in which processing time is minimized while component integrity and performance are enhanced.
It is a further object of the present invention to provide a method and apparatus for forming a cohesive fibrillated polymer electrode component such that the formation process can be carried out continuously.
It is yet a further object of the present invention to provide a method and apparatus for forming a cohesive fibrillated polymer electrode component in which fibrillation of the polymer can be controlled and enhanced.